unsigned int4

I looked in the FAQs, lists, docs, etc but couldn't find an answer to my
question.
Is there a way to specify an unsigned int, such that it would create an
ERROR condition if a transaction
were to attempt to cause a particular value to go negative. This would
be very useful to me.
I would like to be able to use the automatic rollback feature of WORK
blocks if a debit is generated that would
subtract more than it's positive balance. I feel this would be helpful
due to the concurrent nature of our bank
application.

Thanks for any help you can give me.

Scott Jackson (Scott.Jackson@pnl.gov)